The object of the present invention is a sulfur-vulcanizable rubber composition having a base of a copolymer conjugated diene and an aromatic vinyl compound preferably having silica as majority filler, which can be used for the manufacture of high-performance tires in all seasons.
Since savings in fuel and the battle against nuisances created by motor vehicles have become a priority, the purpose of the designers of tires is to produce a tire which has both very little rolling resistance, excellent adherence both to dry ground and to wet and snow-covered ground, very good resistance to wear and, finally, reduced noise of travel.
Numerous solutions have been proposed in order to decrease the rolling resistance of tires, in particular by modifying the rubber compositions used for the treads of the tires. Thus, for rubber compositions which are reinforced with carbon black, it was initially proposed to reduce the content of carbon black. It was then proposed, as in U.S. Pat. No. 4,822,844, to use a carbon black having specific characteristics expressed by a specific iodine absorption surface (IA) and nitrogen absorption surface (N.sub.2 SA), as well as by an average size of well-defined carbon particles. Another solution described in U.S. Pat. No. 4,866,131 proposed the use as tread composition of a copolymer of butadiene and styrene prepared in solution and of low molecular weight in mixture with another conventional copolymer prepared in solution or emulsion. Finally, in U.S. Pat. No. 4,894,420, it was proposed to use a tread formed of a blend of cis 1,4-polyisoprene and a diene/acrylonitrile copolymer. However, none of the solutions proposed up to now has proven satisfactory since the improvement in the rolling resistance is accompanied by a decrease in one or more essential properties, such as the reduction of adherence on wet and/or snow-covered ground or a reduction in the resistance to wear, and, furthermore, all of these solutions are always fully dependent on petroleum. It has also been proposed to use as reinforcing fillers white fillers such as silica, bentonite, clay, titanium oxide, talc, etc., which have the advantage of not being obtained from petroleum and of decreasing the resistance to travel of the tires having a tread comprising such fillers. However, the use of silica in tread compositions has still remained an exception and has frequently represented only a minority fraction of the total filler as described in U.S. Pat. No. 4,894,420 and U.S. Pat. No. 4,820,751 in view of the resultant decline in the properties, in particular the decline in the resistance to wear. In order to remedy this situation, European Patent Application 299 074 proposed a rubber composition comprising silica as reinforcing filler in very large proportions and which is based on a polymer which is functionalized by means of a special alkoxy silane compound having a non-hydrolyzable alkoxy group. However, this solution is restrictive in that it permits the use only of a very specific family of silanes, which constitutes a handicap for industrial use.